1. Field of the Invention
The present invention relates to a page printer control method for printing complicated print data when little memory is available, and a page printer therefor, and relates in particular to a page printer control method for preparing one page of drawing data for a page printer engine, and a page printer therefor.
2. Related Arts
In a page printer, such as an electrophotographic apparatus, a printing unit (engine) forms print images at a constant speed. Thus, a print controller which creates raster image data must send synchronizedly video data to the printing unit with the operation of the printing unit.
Before the printing of each page is started, a conventional print controller, using received data, creates a page of raster image data(drawing data) in memory. Then, while printing, the printer controller starts the operation of the printing unit and reads from the memory and transfers to the printing unit video signals, beginning with the first video signal of a page.
Since according to this technique video signals for one A4 size page are stored at a resolution of 600 dpi, approximately 4 M bytes of memory are required to store one page of raster image data. And as a result, since circuit costs have been reduced by recent advances in LSI circuit construction, the memory which is required accounts for half the cost of a printer controller.
Therefore, a technique has been proposed by which the required memory capacity can be reduced. According to this technique, after each page of raster image data is prepared using received data, the raster image data are compressed, and then the compressed data are stored in memory. Then, to print the compressed raster image data, the data are expanded (decompressed) and the video signals are prepared.
Since according to this method raster image data for one A4 size page are stored at a resolution of 600 dpi, as described above, only half of the memory capacity, i.e., 2 M bytes, is required. Thus, the cost of a printer controller can be considerably reduced.
However, since the compression ratio attained using this technique varies depending on the image which is to be printed, the volume of one page of compressed data changes in accordance with the print image contents. And since the predetermined memory capacity provided for the storage of one page of compressed data is a constant, if the size of the compressed image data for a page containing a complicated print image exceeds the capacity of an area allocated in memory, storage of the data will not be possible, i.e., a memory shortage will occur. And when a memory shortage occurs, printing can not be performed.
To avoid this problem, one method has been proposed whereby raster image data for one page are re-created at a lower resolution and compressed, and the resultant compressed raster image data are stored in memory (e.g., Japanese Unexamined Patent Publication No. Hei 10-305624). When the resolution is reduced, for example, to 300 dpi, the volume of the compressed data is also reduced by half, permitting, thereby, the storage of the data in memory and the continuation of the printing operation.
However, the conventional technique has the following shortcomings.
The conventional technique constitutes a method whereby, when a memory shortage is detected while print data for a specific page are being drawn or compressed, the compression operation is halted, the resolution is reduced, and the pertinent print data are redrawn or recompressed. Thus, when an individual document to be printed is regarded as a print job, a single job frequently involves the printing of a plurality of pages, and if a document (one job) consisting of a plurality of pages is printed in accordance with the conventional method, whereby the resolution used for individual pages can vary, the resolution employed for printing the pages may vary throughout the document. For example, a first and a second page may be printed at a resolution of 600 dpi, while a third page may be printed at a resolution of 300 dpi. Since, as is described above, when printing a single document a variety of resolutions may be used, an overall, unaesthetic appearance is presented by a document printed in accordance with the conventional method. Especially when an official document, such as one for a proposal or for a report, is submitted to a third party, while reading the document the recipient may experience a sense of dissatisfaction.